Last couple of years two of my web hosts silently changed things in the server software/configs, breaking my sites as a consequence. The support did help me fix it right away, but of course only once I found out about it (I don't check these sites daily). I don't keep track of developments in the world of web hosting, so I'm basically wondering if these incidents were just bad luck, or is there some underlying explanation (like what)?

I have no idea what caused the second one, the support gave no explanation and the news page mentions no scheduled updates. I guess I could ask them, but I'm more concerned that they did something than exactly what.

Maybe server software has now reached a point where major revisions (server, control panel etc) have become "desirable", and that many hosts are now migrating at the same time. If so that also begs the question if it's done for security reasons (because the old software can't be patched any further) or because it's fashionable (and will open new vulnerabilities).

Depending on what software it is, users can also demand the latest. I'd say most people don't give a s*** about C-panel and such, but probably more about what version of PHP and Perl is running on the server. It's probably also a selling point to have the latest.

No matter the reason, the host should announce such upgrades/updates and also inform about the effect it may have on sites. The common hostee can't be expected to be updated on such things, but the host should be. IMHO.

Possible due to PHP updates for example if you are using PHP 5.6 then its likely they'll remove it at the end of the year as its classed as "end of life" and server owners dont want compromises so they remove them as a security precaution.